LEARNING GAINS FROM A BRIEF LECTURE/DEMONSTRATION OF MOON PHASES

A single multiple-choice question was used to pre and post-assess a brief lesson on moon phases immediately before and after the lesson in a class for pre-service teachers. The lesson included a lecture on why we see moon phases which involved a classroom demonstration and a diagram showing the relative positions of the sun, the moon, and the earth at the various phases, followed by an explanation of solar and lunar eclipses. The results of the pre/post assessment were very encouraging: 43% answered correctly on the pre-test and 88% on the post-test (a normalized gain of 79%!). The most common distracter chosen on the pre-test was that moon phases were caused by Earth’s shadow (35%).

However, students struggled to answer moon-phase questions on the final exam two weeks later. Two sections had an essay question: “Explain why the moon sometimes appears as a crescent, sometimes as a circle (full moon), and sometimes not at all (new moon).” Only 25% answered correctly (in prose or with a well-labeled diagram). 40% had incomplete explanations or diagrams, several simply stating: “Because the moon has phases.” The remaining 35% were incorrect explanations. However, only 7% of the answers (20% of the incorrect explanations) described moon phases as the result of Earth’s shadow. Other answers included references to Earth’s rotation and a diagram of the solar system with the sun between the Earth and the moon.

Another section was given a multiple-choice question with a diagram of the sun, the Earth, and the moon in a line in that order and a list of moon phases from which to choose. Only 40% of the students answered correctly, approximately the same as on the pre-test for the lesson.

In the short term, the number of students who could choose the best explanation for moon phases on a multiple-choice question increased substantially. Two weeks later, many of those students either could not repeat that explanation or had adopted a new misconception about moon phases.